Many of the newer, curved-mold continuous casting machines employ a rigid or semi-rigid dummy bar. A rigid dummy bar has a radius of curvature equal to the casting radius and is essentially rigid along its entire length. This length is somewhat greater than the distance between the mold and the withdrawal unit which is used to feed the dummy bar into the mold and withdraw it therefrom. Semi-rigid dummy bars are similar but have a flexible portion remote from the mold. The flexible portion makes it possible to store a semi-rigid dummy bar more compactly than a rigid dummy bar.
Dummy bars of the above types are generally stored in racks which are coplanar with and located above the casting path. It is desirable for the storage rack to be somewhat removed from the effect of the heat which radiates from the continuously cast strand. For this reason, the end of the storage rack through which the dummy bar enters and leaves the same is located relatively far from the withdrawal unit.
The withdrawal unit generally includes a movable straightening roll for straightening the strand which tends to maintain the curvature of the mold. This roll is normally located above the casting path and remains in this position until the junction between the strand and the dummy bar has passed by it. The straightening roll is then lowered onto the leading end of the strand to straighten the latter. This action simultaneously causes the strand to be disconnected from the dummy bar.
At the time of disconnection, a major portion of the dummy bar is in the storage rack. The remainder of the dummy bar projects from the storage rack to the junction between the strand and the dummy bar. The projecting portion of the dummy bar transmits the reaction to the force required to disconnect the strand from the dummy bar to the end of the storage rack via which the dummy bar enters and leaves the same. Since this end is located relatively far from the withdrawal unit, the moment generated by the disconnecting force is large, especially when the strand and the dummy bar stick to one another. This moment can result in deformation of the dummy bar thereby causing the latter to be out of alignment with the mold so that the dummy bar can no longer enter the mold. This problem is aggravated in continuous casting machines for small strands such as billets where there is minimal or no guiding structure between the mold and the withdrawal unit.
In a known continuous casting machine, the above problem is alleviated by arranging a support bracket immediately downstream of the straightening roll. The support bracket is rigidly mounted on the base of the withdrawal unit and supports the dummy bar during disconnection of the same from the strand. At the time of disconnection, the junction between the dummy bar and the strand is located between the straightening roll and the support bracket. Since the distance between the straightening roll and the support bracket is short, the moment on the dummy bar is small.
The support bracket straddles the casting path and the strand passes through the support bracket after being disconnected from the dummy bar. However, if the strand should distort for some reason, e.g. due to non-uniform cooling, there is a danger that the leading end of the strand will run into the support bracket. For example, if the strand distorts in such a manner that the leading end of the strand is displaced towards one side of the casting path, the leading end of the strand may come into engagement with a supporting leg of the support bracket. Inasmuch as the latter is rigidly mounted, a number of problems, e.g. damage to the support bracket or a breakout, leading to shutdown of the continuous casting machine could occur.